The invention relates to a fuel injection pump for internal combustion engines including a rotating distributing piston which, during its suction stroke, fills the pump pressure chamber with fuel from a storage compartment. A controlled aperture channel permits removing some of the fuel from the pump working chamber during idling and conditions of reduced engine load.
Most diesel engines produce unpleasantly harsh combustion noises at idling or in the low-load domain. The intensity of these noises may be substantially reduced by prolonging the duration of injection in these rpm regions. In known manner, the injection duration is extended by permitting a portion of the fuel supplied by the fuel pump piston to flow off during the time that the engine operates in this rpm domain. Accordingly, to maintain the engine rpm, this quantity of removed fuel must be replaced, and thus the time during which fuel is supplied is correspondingly extended.
In a known fuel injection pump of the general type described above, the flow control of the efflux channel takes place by means of an annular groove worked into the surface of the fuel pump piston. This annular groove cooperates with a control slide which operates according to the principle of a fluid stop. This known control process, however, may not be applied to commonly used injection pumps because the proper functioning can be guaranteed only when a control slide is present.
In another known fuel injection pump which provides injection time extension during idling by permitting part of the fuel to flow out of the pump's working chamber, the fuel may, in disadvantageous manner, leave the working chamber at the onset of fuel supply. This fact changes the onset of injection and makes the quantity of fuel supplied by the engine incorrect because, even though the efflux is throttled, actual fuel supply to the engine takes place only after sufficient piston pressure has been built up to overcome the opening pressure of the injection valve in the presence of the throttle flow.